Just a thought, why couldnt they be the thickness of an apex seal? Or just a little thicker than they are...Wouldnt this be more effective for sealing, while not adding much more reciprocating mass? And breakage while handling and clearancing wouldnt be a problem!

Ive never broken a new side seal while clearancing but Ive snapped old ones for the hell of it and they are amazingly frail...

 

a little about side seals. they are made by Nippon piston ring, and if that name implies anything its that the side seal is quite literally a piston ring that isn't round.

the pre 85 engines all use a 1mm thick side seal, and it was reduced to .7mm for the FC.

the benefit of the smaller seal is slightly less friction. there is no word on sealing in the Yamaguchi book, but its either the same or better with the smaller seals.

the pre 74 engines used two 1mm thick seals per side, and there isn't much sealing benefit, but there is a friction penalty.

new seals are actually pretty flexible, and old seals aren't, but you're basically reusing a piston ring, so just be more gentle

 

Interesting, didnt realize those specs on the older engines. Also, I suppose the wear on the side housings would be worse with thicker seals, is that the case?

 

hard to say, when they made the side seals smaller, they also added 50hp with the turbo. if anything the turbo engines show more wear everywhere.

 

the wear is likely from the additional power, but even the early engines had plenty of wear with the thicker seals so it seems to have been a push either way.

side seals rarely break once installed, the amount of the seal exposed once the engine is assembled is quite literally a hair. i've only ever seen one fail.

 

I should point out here that all-out race engines are going to .031" piston rings. That's about .8mm. .043" is just about the new standard, that's 1.1mm.

Friction reduction, friction reduction.

 

I'm not sure. Thinner seals do not necessarily mean less friction, basic engineering rules dictate that the amount of surface area does not influence friction resistance. Friction only depends on pushing force and a friction coefficient. Area does not matter. (This also goes for tyres, but that's another story). What does change with thinner seals is that when using the same spring the force per square mm improves because there are less square mm's, which improves sealing while not increasing friction resistance. My guess is that the higher power output of the FC engines called for some improved sealing which caused the use of thinner seals.

 

mazda dropped one set in 1971 .. made them thinner in 1986.. and moved them outboard for the rx8....

in 1971 they found the extra set superfluous.. in 1986 it was about reducing drag and friction .. for the rx8 it was about increasing the port area without letting the ends of the seal float across the port


a thicker seal would run counter to all the above evolution

 

pardon me if we can veer off a bit hear. above explantion is why I find it hard to fully accept the claim 3mm apex wear the housings more than the 2mm specially on moderate reving setups. Doesn't the 2mm have more spring force hence more pressure?

 

Just like piston rings, most of the force comes not from spring tension, but combustion pressure behind the ring/seal.

Think about how engines with poor cranking compression will run just fine after the engine starts, or how the engines have next to no engine braking.

Or how piston engines that suffer detonation can force the rings against the cylinder so hard that the top of the piston breaks off around the ring land.

Larger seals mean more pressure behind them, so more force. The 3mm apex seals have 50% more area behind them so 50% more force on the backside of the seal. Additionally, since the seals are heavier, they're harder to control and more prone to bouncing and chattering, which is torture to rotor housings.

 

more centrifugal weight...

watch a drag radial doing a burnout, you get the basic idea.